cpython interning

cpython-interning.ipynb

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 "cells": [
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Interning range [-5, 256]"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
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     "execution_count": 1,
     "metadata": {},
     "output_type": "execute_result"
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   ],
   "source": [
    "a = 10\n",
    "b = 10\n",
    "\n",
    "a is b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 2,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "c = 500\n",
    "d = 500\n",
    "c is d"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 3,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = 10\n",
    "b = int(10)\n",
    "c = int('10')\n",
    "d = int('1010', 2)\n",
    "\n",
    "a is b is c is d"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### string interning"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 4,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 4,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = 'helloworld'\n",
    "b = 'helloworld'\n",
    "\n",
    "a is b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 5,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = 'helloworld!'\n",
    "b = 'helloworld!'\n",
    "\n",
    "a is b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 6,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "False"
      ]
     },
     "execution_count": 6,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "a = 'hello world'\n",
    "b = 'hello world'\n",
    "\n",
    "a is b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "True"
      ]
     },
     "execution_count": 7,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "### you can force strings to be interned by sys.intern\n",
    "import sys\n",
    "\n",
    "a = sys.intern('hello world!')\n",
    "b = sys.intern('hello world!')\n",
    "\n",
    "a is b"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 13,
   "metadata": {},
   "outputs": [],
   "source": [
    "def compare_without_interning(n):\n",
    "    a = 'a long string that is not interned' * 1000\n",
    "    b = 'a long string that is not interned' * 1000\n",
    "    for i in range(n):\n",
    "        if a == b:\n",
    "            pass\n",
    "def compare_with_interning(n):\n",
    "    a = sys.intern('a long string that is interned' * 1000)\n",
    "    b = sys.intern('a long string that is interned' * 1000)\n",
    "    for i in range(n):\n",
    "        if a is b:\n",
    "            pass"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "comparison took: 15.186233284010086\n"
     ]
    }
   ],
   "source": [
    "import time\n",
    "\n",
    "start = time.perf_counter()\n",
    "compare_without_interning(10000000)\n",
    "end = time.perf_counter()\n",
    "print('comparison took:', end - start)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 15,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "comparison took: 0.28596086699690204\n"
     ]
    }
   ],
   "source": [
    "import time\n",
    "\n",
    "start = time.perf_counter()\n",
    "compare_with_interning(10000000)\n",
    "end = time.perf_counter()\n",
    "print('comparison took:', end - start)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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